A Brisbane mum is furious after finding out that she wouldn't be able to bring her four-month old son – who requires regular breastfeeding due to a medical condition – to an Ed Sheeran concert without buying an extra ticket.

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Kirsty McDonald bought standing tickets to the show last year, the ABC reported. Son Leni was not yet born, and she had planned to attend the show with her mother and sister-in-law.

But new arrival Leni has a lip tie (a condition where the tongue is restricted by a shorter-than-usual band of tissue connecting it to the bottom of the mouth) and will not take a bottle. So McDonald decided she'd bring him along for the ride in a baby carrier (with a pair of earmuffs for protection) to keep feeding him regularly.

When she emailed Ticketek to check this was okay, she was told there was "no free on the knee" (in an email sighted by the ABC).

The problem now is that tickets in McDonald's section for the evening have sold out, so she is unable to purchase another.

There are tickets available for resale on classifieds sites such as Gumtree. But despite Ticketek stipulating that these should not be listed at any price higher than retail value, listings are up to hundreds of dollars more than the original cost. (And in a separate report, the ABC confirmed that Sheeran's Brisbane shows have been the target of ticket fraud.)

McDonald told the ABC that she had not had trouble taking Leni to similar stadium events free of charge in the past.

"I just thought it was absolutely ridiculous. I'm quite angry," she said.

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The ticketing policy was for safety reasons, a spokeswoman for Frontier Touring – the event promoter for the show – told 9Honey on Monday.

She added that the company would not recommend bringing a very young child to such a show in any case, due to the high level of noise and confronting stage and lighting effects.

"It cannot be compared to taking a child to a sporting event," the spokeswoman told 9Honey.

"To date, Frontier Touring have not enforced an absolute ban on infants as we respect the right of a parent or guardian to act in the best interest of their child. We do however enforce the requirement of a ticket purchase for every patron as both a safety and security measure and out of consideration for all attending patrons."

Sarah Lehman, a mother from Broken Hill, told the ABC she took her six-month-old daughter Londyn to Sheeran's Adelaide show (earmuffs also in tow). She said had no problem: in either getting into the concert, or with the levels of – although did appear to have tickets in the seated section.

"As soon as Ed came on [Londyn] literally stopped and chilled out," Lehman said. "She was very, very calm."

Sheeran has been on tour in Australia since the beginning of the month, stopping to meet and greet fans along the way.